Here's another workaround:
If you switch back to "classic email" (in settings) you can file the sent messages with no problem. It certainly is annoying, but that's what I've been doing at the end of the day. Then I switch back to "upgraded" when I'm done.

you can use this work around:
1) make sure you empty your trash box
2) delete the sent messages you want to move
3) open the trash box
4) move the deleted messages from there to the folder of your choise

you can use this work around:
1) make sure you empty your trash box
2) delete the sent messages you want to move
3) open the trash box
4) move the deleted messages from there to the folder of your choise

you can use this work around:
1) make sure you empty your trash box
2) delete the sent messages you want to move
3) open the trash box
4) move the deleted messages from there to the folder of your choise

I am currently having trouble moving emails from my sent folder to individual folders (which i can find later in that particular folder instead of looking through entire sent folder)....i am still able to do the movement from the inbox....why has such changes been made.....now my sent folder is getting large.....

I have reported the same problem from the Main Yahoo comments home page. Haven't received any confirmation, acknowledgement or notification of corrective action. This appears to be a minor issue, but troublesome nonetheless. Please acknowledge and/or correct this issue ASAP.

Here's a stopgap idea until Yahoo fixes this issue. Empty your trash folder and then delete all the emails in your sent folder, then file away these emails from trash to their proper folders! I did this successfully!!!